The present invention relates generally to an insulation technology of a solid rocket motor case, and more particularly to an installation method and an installation apparatus, by which an insulation is adhered to the inner wall near the aft end of the solid rocket motor case.
The propellant used to propel a solid rocket is formed of a plurality of high-energy fuels, oxidizers, and binders. The propellant, when ignited, produces hot gases that spurt from the nozzle of the rock and drive the rocket forward. The hot gases produced in the solid rocket motor have a high temperature ranging from 2400xc2x0 C. to 3700xc2x0C. The structural integrity of the rocket motor case is therefore vulnerable to impairment by such a high heat energy that is accumulated over a period of time within a limited space of the rocket motor case. For this reason, the motor case of various rockets is provided with an insulation device to safeguard the rocket motor case.
The insulation of the rocket motor case is attained in general by means of thin rubber sheet, polymer paste, and coating material. In light of easy installation of the thin rubber sheet, it is widely used to insulate the rocket motor case of a large or medium-sized ballistic or guided missile.
The U.S. Pat. Nos. 4,304,185; 3,347,047; 4,507,165; 4,501,841; and 4,878,431 disclose various preparations of rocket motor case insulation materials in the form of rubber coating or strip. These insulation materials are adhered to the inner wall of a rocket motor case by a specific mechanical method. In the case of the insulation materials in the form of the rubber coating or paste, the adhesion of the rubber coating or paste is attained respectively by spray coating or paring. As far as the application of the rubber strip is concerned, the adhesion of the rubber strip is achieved by various methods, such as inflatable mandrel technique, molding technique, manual lay-up technique, strip winding technique, etc.
In view of the fact that the aft end of a rocket motor case is provided with a nozzle section, the insulation of the rocket motor case poses a technical problem. The nozzle section of the rocket motor case has an inner diameter which is abruptly reduced, thereby resulting in a steep increase in pressure of hot gases produced by combustion of the rocket propellant. As a remedial measure, the thickness of the insulation located at the aft end of the rocket motor case is appropriated increased. In light of the geometrical change in profile of the aft end in relation to the motor case, the technical difficulties involving the insulation adhesion of the aft end of the rocket motor case is further compounded. For example, the insulation material cannot be securely adhered to the curved portions of the rocket motor case by the conventional manual lay-up technique. In addition, such conventional technique often results in the left-over of gas bubble residue between the insulation and the inner wall of the rocket motor case.
With the purpose of overcoming the deficiencies of the prior art methods described above, it is the primary objective of the present invention to provide a novel apparatus which is designed to adhere securely an insulation to the aft end of a rocket motor case. By using the apparatus of the present invention, an pre-molded insulation loop can be precisely located at the aft end of the rocket motor case. The insulation loop is formed by casting and is partially cured. Upon having been located at the aft end of the rocket motor case, the partially-cured insulation loop is exerted on by a pressure before it is subjected to a heat treatment to bring about the post-curing of the insulation loop. The insulation loop is thus securely attached to the inner wall of the rocket motor case.
It is another objective of the present invention to provide a novel method of installing an insulation in the aft end of a rocket motor case. The method of the present invention involves a first step in which a rubber strip is made into a rubber loop by casting. The rubber loop so made is then partially cured. The partially-cured rubber loop is adhered to the inner wall of the aft end of the rocket motor case. Thereafter, the insulation rubber loop is pressed and heated to bring about the post-curing of the insulation rubber loop and the attaching of the insulation rubber loop to the inner wall of the aft end of the rocket motor case. The cured insulation rubber loop installed by the method of the present invention is relatively effective in providing the rocket motor case with protection against the thermal breakdown or deformation of the rocket motor case.
It is appropriate to describe in detail here the advantages of the present invention over the prior art methods described above. The most simple and feasible method of the prior art is the manual lay-up technique, which has a serious drawback attributable to the property of a material of which the insulation is made, and the dimension of the rocket motor case. For example, an insulation material containing a large amount of fiber tends to have a greater toughness, which is the culprit of the technical difficulty of the manual lay-up technique of the prior art. As far as the dimension of the rocket motor case is concerned, it is conceivably difficult for a worker to install the insulation in the rocket motor case of a small dimension. In addition, it is uncomfortable and even hazardous for a worker to install the insulation in a confined workplace. The quality of the work done by the worker in such a hazardous environment is therefore subject to scrutiny.
According to the present invention, the casting and the partial curing of the insulation material are done outside a rocket motor case. The partially cured insulation has a fixed form and hardness, thereby making the insulation less vulnerable to deformation in the course of installation of the insulation.
The prior art methods are further handicapped by the fact that the insulation installation cannot be done easily and effectively in the aft section of a rocket motor case, due to a relatively small diameter and a curved profile of the aft section. In the course of a manual installation of the insulation in the aft section, it is difficult for a worker to apply a pressure evenly on the insulation to against the inner wall of the aft section in a consistent manner. As a result, air bubbles are bound to be trapped between the insulation and the inner wall of the motor case. The air bubble residue undermines the adhesion at the interface of the insulation and the inner wall of the aft section. The char forming insulation at a high temperature is susceptible to being stripped off the inner wall of the aft section by the strong gas flow that is produced as a result of combustion of the rocket propellant.
The present invention averts the trapping of air bubbles at the interface of the insulation and the inner wall of the aft section, thanks to the apparatus of the present invention by which a silicone rubber block is used to press a precast insulation rubber loop that has already been properly located. The insulation is therefore secured to the inner wall of the aft section. It is therefore readily apparent that the present invention is efficient and cost-effective.
The features and the advantages of the present invention will be more readily understood upon a thoughtful deliberation of the following detailed description of a preferred embodiment of the present invention with reference to the accompanying drawing.